Chemical treatment of metal

ABSTRACT

A method for preparing metal surfaces for receipt of a coating such as a paint or adhesive whereby increased coating adhesion and corrosion resistance is achieved and the treated metal per se, are disclosed. The method comprises contacting the metal surface with various phosphine oxides.

Umted States Patent [191 {111 3,770,513 Wystrach Nov. 6, 1973 CHEMICAL TREATMENT OF METAL [56] References Cited [75] Inventor: Vernon Paul Wystrach, Wilton, UNITED ES PA NTS C0nn- 3,622,401 ll/l97l McCullough l48/6.l5 R

73 A A C d C sslgnee g i ggfg i ig ompany Primary Examiner-Ralph S. Kendall Attorney-Frank M. Van Riet [22] Filed: June 8, 1972 211 App]. No.: 260,953 1 ABSTRACT A method for preparing metal surfaces for receipt of a U S 148/6 15 R 106/14 252/389 coating such as a paint or adhesive whereby increased {48/31 148/6 coating adhesion and corrosion resistance is achieved [51] Int Cl 2:23 2 and the treated metal per se, are disclosed. The method Fieid R 31 5 comprises contacting the metal surface with various phosphine oxides.

10 Claims, No Drawings CHEMICAL TREATMENT OF METAL BACKGROUND OF THE INVENTION The use of various chemical materials in the treatment of metal surfaces is well known to those skilled. in

the art. For example, US. Pat. No. 3,615,888 describes a method wherein various diketones are utilized in the surface treatment of metal, whereas U.S. Pat. No. 3,615,889 discloses the use of various quinolines for the same purpose. Phosphinyl derivatives are set forth in US. Pat. No. 3,615,894 and phosphinic and phosphonic acids are mentioned as useful in US. Pat. No. 3,624,146.

Another patent which discloses a method even more closely related to that of the instant invention is US. Pat. No. 3,622,401 wherein various straight chain hydroxypropyl phosphine oxide derivatives are shown.

SUMMARY 1 have now found that the adhesion of coatings to metals can be materially increased or strengthened by treating the metal with a chemical material which is either chemically reacted with the metal or absorbed thereby via strong bonds. As set forth in the abovedisclosed patents, a foundation or integral chemical or chemically bonded coating is formed on the metal surface, which foundation is then more susceptible to an ultimate or surface coating applied thereto, such as a paint or adhesive. My method results in coatings which are securely bonded or adhered to the foundation layer because the foundation is chemically bonded to the metal and any ultimate coating is chemically bonded to the foundation. That is to say, upon treating the metal surface according to my novel method, a reaction causes a strong bonding of the phosphine oxide derivative to the metal, the phosphine oxide derivative layer having a free group which is capable of reacting with an exterior surface coating. This free reactive group chemically combines with available groups of the coating to produce an article of manufacture having a tightly bonded coating thereon. Additionally, the corrosion resistance of metals treated according to the present invention is at least as effective as, and in many cases, better than commercially available corrosion resistance systems.

DESCRIPTION OF THE INVENTION INCLUDlNG PREFERRED EMBODIMENTS My novel process comprises treating a metal surface, such as that of aluminum, steel, carbon steel, iron, titanium, and the like with a phosphine oxide'derivative having the formula I R -CHOH oxide layer formed on the surface of the metal to be treated. The existence of such oxide layers is well recognized by cogent workers in the: art. Such layers form upon exposure of the metal to the atmosphere. After the phosphine oxide derivative-metal oxide bonding is complete, the remaining reactive groups of the phosphine oxide foundation layer are then free to react with available groups of the surface coating, i.e., paint, adhesive etc. applied thereto, thereby chemically bonding the coating to the metal. The phosphine oxide derivative-metal oxide bonding is pseudo-chemical in nature and can be more accurately described as a chemisorption or chelation of the derivative by the metal.

The phosphine oxide derivative foundation layer may be applied to the metal surface, the metal first being thoroughly cleaned such as by degreasing with trichloroethylene etc. or other common techniques, by immersing, dipping, painting, brushing, wiping, spraying etc. the metal to be treated with solutions of one or more of said phosphine oxide derivatives, for a length of time such that the metal surface absorbs or reacts with a sufficient amount of the derivative. The metal is then merely removed from the solution and allowed to dry.

Additionally, the phosphine oxide derivative can be applied to the metal by first incorporating it into the surface coating material, e.g., the paint or adhesive, and then applying the surface coating to the metal. In this manner, the phosphine oxide derivative can be added, for example, to the paint vehicle, and the paint then can be sprayed etc. onto the metal. Similarly, the phosphine oxide derivative can be added to one part of a two-part adhesive system and the adhesive can then be applied to the metal. In each instance, the reactive groups of the surface coating material will react with the appropriate groups of the phosphine oxide derivative while the derivative itself reacts with the oxide on the metal surface, as more specifically described above. The solution of the hydroxyalkyl phosphine oxide derivative can comprise from about 1 part to about 50 parts of the derivative per 1,000 parts of solvent, e.g., ethanol, methanol, water, etc. The treatment is preferably conducted at room temperature although higher or lower temperatures may be utilized, if desired. Complete chemisorption of the phosphine oxide derivative onto the metal surface is generally achieved in from about 10 to about 20 minutes, the: lower the derivative concentration, the longer the reaction time necessary.

As mentioned above, because a. group reactive with the surface coating or layer is present on the phosphine oxide derivative there is afforded a chemically available site whereby the reactive group of a paint or adhesive layer may chemically react to thereby form a tightly adhering coating or layer. Examples of paints, adhesives or other coatings which may be used include epoxy paints and adhesives, i.e. those containing chemically available groups; urethane paints and adhesives, i.e. those containing chemically available NCO groups; acrylic paints and adhesives; i.e. those containing chemically available groups; vinyl paints and adhesives, i.e. those containing chemically available -CH=Cl-I- groups and the like. As

groups are explicitly represented, as discussed above,

by the amino, OI-I, SH, COOl-I, epoxy and unsaturated aliphatic substituents and in the case of epoxy and urethane paints and adhesives would be amino, -OH, -SH,

-COOH or epoxy substituted groups, while in the case of acrylic or vinyl paints and adhesives, the reactive group of the phosphine oxide derivative would be the alkenyl substituent, including vinyl, allyl etc.

The coating, e.g., a paint, can be applied in a condition such that the reaction occurs while the paint vehicle evaporates or in a condition such that the paint must more completely polymerize or cure before it forms a useful coating. In the latter case, if a functional group of the phosphine oxide derivative is such that it initiates polymerization of the paint, the paint may be applied in a prepolymer' or semipolymer condition. An example of such a treatment is illustrated by the use of a hydroxy group containing derivative and an epoxy prepolymer. ln this case, the hydroxy group both reacts with and cures (polymerizes). the epoxy prepolymer.

Additionally, I have found that my novel processing procedure can be utilized in conjunction with known procedures to obtain a pseudosynergistic effect. For example, I can improve the corrosion resistance of metals treated according to my invention by first treating the metal with an inorganic chromate in a manner known in the art. Furthermore, the chromate (e.g., potassium dichromate; chromic acid solution, etc.) may be incorporated into the solution of the phosphine oxide derivative before treating the metal according to my invention. In this manner, the corrosion resistance of the metal is further increased without loss of the enhanced surface coating adherence mentioned above.

The hydroxyalkyl phosphine oxide derivatives utilized in the present invention are well known to those skilled in the art as are methods for their production. They may be produced according to procedures set forth in Kosolapoff; Organophosphorus Compounds; J

Wiley and Sons; pgs. 10l05; 1950. Generally, the procedure may consist of reacting an appropriately substituted primary or secondary phosphine (Rauhut et al.;

Jour. Org. Chem; Vol. 26; pg. 5138; 1961 with appro- 50 priately substituted amines, diols or Grignard reagents etc. at temperatures ranging from about 50C.-90C. in

the presence of a free-radical generating catalyst and oxidizing the resultant tertiary phosphines as is known in the art to the corresponding phosphine oxide. Additional derivatives which may be utilized in the instant procedure are prepared as set forth in US. Pat. Nos. 3,067,258 and 3,099,684, which references, and those specified above, are hereby incorporated herein by reference.

The pretreating process and products of the instant invention find utility in military, industrial and consumer fields such as aircraft and ship surfaces, cooling towers, heat exchangers, window screens, siding and t slise- The following examples are set forth for purposes of illustration only and are not meant to be construed as limitations on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

Example 1 Aluminum panels, 3 X 5 inch, are degreased by dipping in benzene and further cleaned by dipping in a hot 10 percent solution of a commercially available aluminum cleaner. The panels are then allowed to dry in air. One panel is then immersed in a solution of tris(hydroxymethyl)phosphine oxide in ethanol. After 15 minutes the panel is removed and allowed to dry.

, The panel is then spray painted with a commercially available epoxy paint and allowed to dry and cure for 5 days at room temperature.

moved sharply with a pull at right angles to the test surface. A visual examination allows a reasonably accurate estimation of the percent finish remaining on the panel in the test area.

The above-treated panel showed substantially superior adhesion in comparison with a control panel which was not pre-treated with phosphine oxide before coatmg.

The average results of tests conducted on panels treated according to Example 1, in addition to the results recorded utilizing different hydroxyalkyl phosphine oxide derivatives according to the process of the present invention, are set forth in Table 1, below.

' At least percent of coating removed. 2 At least percent of coating retained. *No phosphine oxide. Acrylic paint used.

I claim: Y i. A method which comprises treating a metal surface with a compound having the formula surface is treated with said compound and a surface coating chemically reactive with said compound is coated thereon.

4. A method according to claim 1 wherein said compound is added as a mixture with a surface coating re active with said compound.

5. A method according to claim 1 wherein said compound is tris(hydroxymethyl) phosphine oxide.

6. A method according to claim 1 wherein said metal is aluminum.

7. A method according to claim 3 wherein said surface coating is a paint.

8. A method according to claim 4 wherein said surface coating is paint.

9. A method according to claim 3 wherein said surface coating is an adhesive.

10. An article according to claim 2 wherein said metal is aluminum. 

2. An article of manufacture comprising a metal surface having coated thereon a compound having the formula set forth in claim
 3. A method according to claim 1 wherein the metal surface is treated with said compound and a surface coating chemically reactive with said compound is coated thereon.
 4. A method according to claim 1 wherein said compound is added as a mixture with a surface coating reactive with said compound.
 5. A method according to claim 1 wherein said compound is tris(hydroxymethyl) phosphine oxide.
 6. A method according to claim 1 wherein said metal is aluminum.
 7. A method according to claim 3 wherein said surface coating is a paint.
 8. A method according to claim 4 wherein said surface coating is paint.
 9. A method according to claim 3 wherein said surface coating is an adhesive.
 10. An article according to claim 2 wherein said metal is aluminum. 